1. Field of This Invention
This invention relates to the field of biodegradable polymers and processes of preparing such.
2. Prior Art
The disposal of polymers was not a major problem prior to 1940 as the usage of polymers per capita was relatively low. Besides the major thermoplastic resins were essentially regenerated cellulose and various cellulose derivatives (which were also the main packaging materials at that time) and the main fiber for apparel, etc., was cotton cellulose of rayon. These cellulosic componds are completely biogradable. A wide variety of soil and marine microorganisms have the ability to enzymatically hydrolyze cellulose to soluble intermediates, which in turn serve as a carbon source for microbial and fungal growth. As a result, the waste cellulosics were removed from the environment and there was little or no disposal problem. However, since the 1940's a large variety of new synthetic polymers (having many varied properties) have been synthesized and have been used to package every conceivable item. In addition, the use of man-made fibers exceeds that of cotton fiber in the United States and is nearly equal to cotton fiber usage world-wide. Almost without exception, the synthetic polymers (including man-made fibers) used today are non-biodegradable. This has created a large disposal problem which is having a serious ecological and environmental impact. The preparation of biodegradable synthetic polymers would be of considerable importance of resolve the social and economic problems caused by the wide-spread use of synthetic polymers.
Polyethylene, polypropylene and polyvinyl chloride, the leading packaging resins, are all inherently unstable, but this property alone would make them unsuitable for packaging. So additives have to be added to make them stable but this makes them stable when thrown out as waste or litter.
Heap, Wendy M., et al., "Microbiological Deterioration of Rubbers and Plastics", J. Appl. Chem., Vol. 18 (July 1968 ), pp. 189-194, reviews the microbiological deterioration of rubbers and plastics. To some degree, many synthetic and naturally-occuring polymers are stated to be attacked, but it is not possible to say which chemical group in each polymer is susceptible. Heap et al. states: that cellulose plastics such as the acetate, acetate-butyrate, and propionate, as well as ethyl cellulose and benzyl cellulose are reported to be fairly resistant to attack by micro-organisms, although their susceptibility can be affected by the type of plasticiser used; and that this is in contrast to cellulose and cellulose nirate which appear to be appreciably susceptible to fungal growth. To close the report, Heap et al. stated that the main conclusions which can be drawn from this review are that the available evidence is confused, contradictory and in some cases misleading.
Worne, Howard E., "Modern Plastics For Degradability", Plastic Tech., (July 1971), pp, 23, 26 and 28, sets out many of the problems associated with plastics waste disposal. Worne states cellulosics originally used for most transparent packaging are biodegradable. A wide variety of soil and marine micro-organisms enzymatically hydrolyze the insoluble cellulose to intermediates which in turn serve as a source of carbon for fungal growth. The cellulosics are basically ultraviolet light stable and cannot be easily degraded in sunlight.
Almost all of the new synthetic polymers have, with almost no exceptions, polymer structures with configurations that cannot be broken down by soil microorganisms, and which lack the necessary constitutive enzyme systems capable of biodegrading these polymers.
"Biodetermination of Plastics", SPE Trans., (July 1964), pp. 193-207, is a review of the efect on non-cellulosic plastics of attack by various organisms. But Table 1 on page 198 states that cellulose acetate has poor to good microbial resistance depending upon the degree of acetylation -- see also pages 206 and 207.
Rodriguez, F., "The Prospects For Biodegradable Plastics", Chem. Tech., (July 1971), pp. 409-415, teaches that cellulose decomposes readily when attacked by a wide variety of microorganisms.
U.S. Pat. No. 3,386,930 teaches filaments prepared from copolymers containing soft and hard segments. The hard segments are cellulose triacetate and the soft segments are certain diisocyanates.
U.S. Pat. No. 3,364,157 discloses block and graft copolymers containing at least one segment of an oxymethylene polymer. Such block and graft copolymers have modified strength characteristics, flow characteristics, solvency, crystallinity, and thermal stability. The copolymer can have the structure: ##EQU3## wherein P.sub.x is an oxymethylene polymer segment, P.sub.y is a dissimilar organic polymeric segment, X is an atom selected from the group consisting of oxygen and sulfur atoms, R.sub.1 is an organic radical selected from the group consisting of divalent and trivalent aliphatic cycloaliphatic, and aromatic radicals having up to about 20 carbon atoms, W is selected from the group consisting of --O--, --S--, ##EQU4## where R.sub.3 is selected from the group consisting of hydrogen, halogen, and alkyl having one to five carbon atoms, m and n are integers from one to two, m+n is an integer from two to three, and Z is an integer from one to 100. P.sub.y can be cellulose or its derivatives, such as, the cellulose esters. To show that biodegradable polymers were not even contemplated, column 5, lines 62 to 69, the peferred polymeric co-blocks includes cellulose esters having an acetyl value of between about 50 and 62 percent.
U.S. Pat. No. 3,821,136 teaches a polyurethane polymer which can be used, for example, as a controlled release agent. Such polymers have pronounced hydrophilicity. U.S. Pat. No. 3,316,186 discloses certain quick drying printing inks which include a polyol prepolymer, a diisocyanate prepolymer, and a reactive polymeric resin hardener.
U.S. Pat. No. 3,475,356 teaches certain solvent resistant cross-linked polymers prepared from an ester of cellulose with at least one alkanoic acid, a particular linear saturated synthetic polymer and a particular organic diisocyanate.
U.S. Pat. No. 3,386,931 teaches certain copolymers which are the reaction products of an organic diisocyanate, a non-cellulosic polymer containing terminal functional groups, and a high-molecular-weight cellulose triester of a lower aliphatic acid. It also teaches graft polymers which are the reaction products of the last two above-mentioned reactants.
Taylor, Lynn J., "Polymer Degradation: Some Positive Aspects" Chem. Tech., (Sept. 1973), pp. 552-559, which is not prior art against this invention, surveys the entire polymer degradation field. Taylor teaches that cellulose and cellulose ethers are generally biodegradable.
A comprehensive review of the field of block copolymers is found in "Block Copolymers", D. C. Allport and W. H. Janes, Ed., John Wiley & Sons, New York, 1973. Among the many methods of synthesis, the use of diisocyanates as coupling agents for polymeric diols and other difunctional polymers has been investigated -- see D. C. Allport and A. A. Mohajer in "Block Copolymers," ibid, ch. 5. This method has been extended to cellulosic blocks using cellulose triacetate oligomeric species having hydroxyl end-groups which are capable of reacting with polyester, polyether, or other polymers containing hydroxyl or other functional end-groups by coupling with organic diisocyanates. See Steinmann, H. W., Polym. Prepr., 11 (1), 285 (1970) and U.S. Pat. No. 3,386,932 (H. W. Steinmann). Such copolymers are interesting because of their novel properties, for example, Steinmann has prepared elastomeric fibers from his block copolymers.
U.S. Pat. No. 2,836,590 discloses an improvement in the partial decetylation of organic acid esters of cellulose by alcoholysis.
No prior art is known which teaches the deacylation of cellulose triacetate oligmer block copolymers let alone that such are biodegradable polymers.